This invention pertains to a beam alignment device for use with diagnostic x-ray apparatus.
In one type of diagnostic x-ray apparatus the x-ray tube is mounted inside of the body of the patient's supporting x-ray table. An image receptor such as an image intensifier or a radiographic film is mounted above the table top in such manner that the image receptor may be moved toward and away from the x-ray tube. In this arrangement, it is necessary to have the central ray of the beam, which diverges from the focal spot of the tube, perpendicular to and centered on the plane of the image receptor. As is well known, if the central ray is not perpendicular and centered, the central ray will shift laterally along the receptor plane as the plane is raised and lowered relative to the focal spot. A consequence is that the edges of the collimated x-ray beam will not coincide with the edges of the receptor plane at all levels. Thus, the beam may fall short of the edge of the receptor plane on one side and overlap on the other side, which in the latter case, results in part of the x-ray image being cut off and not recorded. This is undesirable, not only because of the loss of information in the image, but also the patient is exposed to radiation dosage which produces no information.